1. Field
The present invention applies to the field of launch systems for small space payloads and, in particular, to deploying a small payload from the exterior of a space launch vehicle.
2. Background
Commercial, scientific and educational institutions are developing or have developed very small satellites, spacecraft and space instruments. These new small devices have a wide range of applications and uses. One goal of such small satellite development programs is to lower the cost and development cycle time as compared to conventional earth-orbiting and interplanetary spacecraft. Costs are reduced primarily through simplification and miniaturization. The number of functions as well as the length of the mission can be reduced to lower costs.
Small spacecraft have been classified into different types. The current classifications are not precise or controlling but indicate the variety of very small spacecraft. New spacecraft are under development which may or may not fit into any existing category. Smallsats are typically considered to be small spacecraft or small satellites weighing less than about 200 kg. Nanosats, “nano-spacecraft” or “nano-satellites” are typically considered to be a particularly small category of smallsats which might weigh between 1 kg and 10 kg. Other smallsats can be smaller still. The CubeSat Project is a collaborative effort between California Polytechnic State University San Luis Obispo, and Stanford University's Space Systems Development Laboratory. It provides a standard for the design of smallsats so that a common deployer is used. Currently more than 30 high schools, colleges, and universities from around the world are developing CubeSats. The CubeSat standard specifies each satellite as a 10 cm cube of 1 kg maximum mass and provides additional guidelines for the location of a diagnostic port, remove-before-flight pin, and deployment switches. For reference, a typical commercial communications satellite weighs over 3,000 kg.
Smallsats, if they can be launched inexpensively and with a short development and integration time offer a new era in space science, development and exploration. Launch costs are generally a function of size (both mass and volume), so smaller payloads should be cheaper to launch. While many organizations have built or are building Smallsats, there is no inexpensive and quick way to launch such small payloads. As a result, many of the advantages of smallsats are lost. Current launch vehicles are designed for large, heavy, and expensive payloads on the order of 2,000 kg and up.
Some nanosats have been released from the Space Shuttle cargo bay, these launches required individual human attention and special provisions within the Space Shuttle cargo bay. Smallsats have been launched on conventional expendable launch vehicles, and the Delta, Pegasus, and Ariane programs have developed special adapters to carry secondary payloads within their primary payload fairings. However, for each such launch, a great amount of customization, analysis, and safety review is required for each smallsat.
The most developed and readily available smallsat launcher is the Ariane Structure for Auxiliary Payloads (ASAP). For Ariane 5, the ASAP can carry up to eight satellites weighing up to 80 kg each, or up to four satellites weighing 300 kg each within the primary payload fairing. However, launch vehicle preparations still require 12 to 24 months. This is often longer than the development time for the payload itself. The ESPA ring being developed for Delta IV and Atlas 5 will not launch until 2005 at the earliest, partly due to the difficulty of coordinating its various secondary payloads. Both ESPA and ASAP interact significantly with their respective rockets because they are placed directly in the load path with the primary payload.